Method of treating Ti-Nb-Zr-Ta superconducting alloys

ABSTRACT

A superconducting metal alloy is formulated from 10- 50 at % Ti, 20-50 at % Nb, 10- 40 at % Zr and 5- 12 at % Ta. A Ti-Nb-Zr-Ta superconducting alloy with a fine, non-homogeneous structure is obtained by forming a Beta solid solution of said Ti-Nb-Zr-Ta alloy by heating the alloy to a temperature within the Beta solid solution range, cooling and then cold working said heated alloy, heating said cold worked alloy to a temperature within the ( Beta &#39;&#39;+ Beta &#39;&#39;&#39;&#39;) alloy to maintain the peritectoid structure, cold working the peritectoid alloy, heating said peritectoid alloy to a temperature within the eutectoid range to form a multiphase eutectoid alloy structure and then cooling said eutectoid alloy and finally cold working the eutectoid alloy.

United States Patent 1 Horiuchi et a1.

[ METHOD OF TREATING Ti-Nb-Zr-Ta SUPERCONDUCTING ALLOYS [75] Inventors:Takefumi Horiuchi, Kobe; Yoshiyiki Monju, Nishinomiya; Isamu Tatara,Kobe; Nobuyuki Nagai, Kobe; Manabu Hisata, Kobe; Kiyoshi Matsumoto,Kobe, all of Japan [73] Assignee: Kobe Steel, Ltd., Kobe City, Japan[22] Filed: Sept. 17, 1973 [21] Appl. No.: 397,866

[52] US. Cl 148/12], 75/134 R, 75/134 N, 75/174, 75/175.5, 148/11.5F,148/32.5 [51] Int. Cl. C22f l/l8 [58] Field of Search... 75/134 R, 134N, 174, 175.5; 148/l1.5, 12.7, 133, 32, 32.5

[56] References Cited UNITED STATES PATENTS 2,822,268 2/1958 Hix 75/1743,038,798 6/1962 Berger et a1. 75/174 3,408,604 10/1968 Toshio Doi eta1. 75/174 X 3,671,226 6/1972 Komata et a1. 75/174 FOREIGN PATENTS ORAPPLICATIONS 243.841 10/1969 U.S.S.R 75/l75.5

TEMPERATURE (U T lxlo hURK/NG 41/0 HEAT msAr/m moosss [4 1 Feb. 18,1975

OTHER PUBLICATIONS Journal of Applied Physics, Vol. 38, 1967, page 903and 904.

Superconducting Materials, Savitskii et al., Plenum Press, NY. 1973,pages 350 and 351.

Primary ExaminerC. Lovell Attorney, Agent, or Firm-Ob10n, Fisher,Spivak, McClelland & Maier [57] ABSTRACT A superconducting metal alloyis formulated from 1050 at Ti, 20-50 at Nb, 10-40 at Zr and 5-12 at Ta.A Ti-Nb-Zr-Ta superconducting alloy with a fine, non-homogeneousstructure is obtained by forming a [3 solid solution of said Ti-Nb-Zr-Taalloy by heating the alloy to a temperature within the B solid solutionrange, cooling and then cold working said heated alloy, heating saidcold worked alloy to a temperature within the (B+B") alloy to maintainthe peritectoid structure, cold working the peritectoid alloy, heatingsaid peritectoid alloy to a temperature within the eutectoid range toform. a multiphase eutectoid alloy structure and then cooling saideutectoid alloy and finally cold working the eutectoid alloy.

1 Claim, 8 Drawing Figures Pmmzn im 3.867.209

sum 10F a TEMPERATURE ("U T WORK/N6 AND HEAT mar/N6 PROCESS o r 60/(0eMk l l l 0 l0 30 I00 300 I000 SECOND 'SMGE INTERMEDIATE HEAT 0*- F/Q ZTREAT/N6 rm? (HIT/(AL CUR/E'NT VALUE I (A/025'mmfl) Q P D a o J i IMETHOD OF TREATING Ti-Nb-Zr-Ta SIIFE RifONIiUCTllTG ALLOY? BACKGROUND OFTHE INVENTION Field of the lnvention Description of the Prior ArtSuperconducting alloys formed from Ti-Nb, Nb-Zr and Ti-Nb-Zr mixturesare well known. The critical current density, Jc, of thesesuperconducting alloys can be increased by various known techniques,such as for example, a final low temperature aging treatment afterstrong working of the Ti-Nb alloys, a strong working treatment of theNb-Zr alloys and a multi-phase heat treatment of the Nb-Zr-Ti alloys.Japanese Patent application Publication No. 14,028/68 has proposed amulti-phase heat treatment for Ti-Nb-Zr alloys. This treatment has thedisadvantage that when it is desired to conduct a multi-phase heattreatment in the working process as an intermediate heat treatment, thedensity Jc at low magnetic fields is low. If, however, it is desired touse the multi'phase heat treatment in the final heat treatment stage,the density Jc of the medium and the high magnetic fields of the alloysdecrease. Further, the optimum heat treatment temperature formulti-phase heat treating the Ti-Nb-Zr alloys is a relatively hightemperature of about 700C. When operating at these temperatures,however, certain percautions must be taken. That is, these kinds ofsuperconducting alloys are coated with copper after the [3 solidsolution treatment, and then worked and heat treated. During the heattreatment at temperatures greater than 700C, a reaction between thesuperconducting alloy and the copper coating occurs which producescertain undesirable results. Thus, the multi-phase heat treatment whenused on these alloys should be conducted before being coated withcopper.

Other conventional superconducting materials have also been known, suchas the solid solution alloys of Ti- Nb, Nb-Zr, and Ti-Nb-Zr as well ascompounds such as Nb Sn, V Ga, NbN, and the like. These superconductingalloy compositions have various advantages and disadvantages. Forexample, the Ti-Nb alloy has a relatively high critical magnetic field(about 120 K06), but when its external magnetic field is less than 40KOe, the critical current value thereof is not very substantial. On theother hand, the Nb-Zr alloy has a large critical current value atmagnetic fields less than 40 KOe in relation to the external magneticfield. However, the critical current value is small when the criticalmagnetic field is less than 70 KOe. Furthermore, the critical magneticfield and the critical current of these superconducting compounds areexcellent, but the technique of manufacturing these materials isdifficult and expenme.

A need, therefore, continues to exist for a superconducting alloy whichis more readily and less costly pr duced while simultaneously havingexcellent superconducting characteristics from low to high magneticfields.

SUMMARY OF THE INVENTION Accordingly, one object of the presentinvention is to provide a method for treating superconducting alloyswhich gives alloys which have excellent superconducting characteristicsat low magnetic fields as well as the medium and high magnetic fields.

Another object of the present invention is to provide a method fortreating superconducting alloys to provide alloys which have excellentworkability and mechanical properties.

Yet another object of the present invention is to provide asuperconducting alloy which has excellent superconductivity, workabilityand mechanical characteristics at low magnetic fields as well as atmedium and high magnetic fields.

Briefly, these objects and other objects of the present invention ashereinafter will become more readily apparent can be attained byproviding a Ti-Nb-Zr-Ta alloy with a fine, non-homogenous structure byforming a solid solution of the Ti-Nb-Zr-Ta alloy by heating the alloyto a temperature within the B solid solution range, cooling and thencold working the heated Ti-Nb Zr-Ta alloy, heating the cold worked alloyto a temperature within the (B'+B") phase region and then cooling theheated (,B'B")alloy to maintain the peritectoid structure, cold workingthe peritectoid alloy, forming a multiphase B'+B"+oz(m) eutectoid alloystructure by heating the peritectoid alloy to a temperature within the(B'+B"- B'+B"+a(+w)) eutectoid structure range and then cooling theeutectoid alloy and cold working the eutectoid alloy. A Ti-Nb-Zr-Tasuperconducting alloy is also provided which comprises 110-50 at Ti,20-50 at Nb, 10-40 at Zr and 5-l2 at Ta.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of theinvention and many of the attendant advantages thereof will be readilyobtained as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a diagram showing a T.T.T. curve of a cold worked Ti-30 atNb-30 at %Zr7 at Ta alloy;

FIG. 2 is a diagram which shows the influence of the phase separationheat treatment time on the two phase heat treatment as a parameter ofthe critical current value of the Ti-30 at Nb-30 at Zr-7 at Ta alloyFIG. 3 IS a diagram which shows the influence ot the a phaseprecipitation heat treatment time to the X-ray integrated intensity ofthe a phase and the In phase of the Ti-30 at Nb-30 at Zr-7 at Ta alloy,and to the critical current value;

FIG. 4 IS a diagram which shows a comparison of the FIG. 5 is a diagramwhich shows the superconducTirig characteristics, i.e., the criticalmagnetic field, of various Ti-Nb-Zr-Ta quaternary alloys;

FIG. 6 is a diagram which shows the superconducting characteristicsi.e., the critical magnetic field of a quaternary alloy containing 30 atNb and 30 at% Zr in which the Ti and Ta content is continuously changed;and

FIG. 7 is a diagram which shows the realtion between the externalmagnetic field and the critical current value of a material of thepresent invention in comparison to the relationship of the sameproperties of another conventionally available superconductiong alloy.

3 DESCRIPTION or THEPREF'ERR'I'QD EMBODIMENTS FIG. 1 showsthe T.T.T.curve of a 90% cold worked Ti-30 at Nb-30 at Zr-7 at Ta superconductingbecause Ta has an inhibiting effect on the a(+w) phase precipitation,which results in a delay in the precipitation of the a(+w) phaseseparation and the peritectoid region is enlarged. This observation isessential for the development of the heat treatment of the presentinvention. In the treatment of the metal the peritectoid heat treatment,which has not been performed, and the a phase precipitation heattreatment are independently conducted. The peritectoid heat treatment isconducted for a short period of time at a comparatively low temperaturebecause of pre-working the alloy. The a phase precipitation heattreatment is conducted at a low temperature for only a short period oftime by' working, and the structure is finely refined andnonhomogenized. Further, in the a phase precipitation heat treatment,precipitation of the to phase occurs. In particular, when the a phaseprecipitation heat treatment is conducted for only a short period oftime, the a phase becomes an a (+11)) phase.

The present invention will be explained in more detail with reference tothe working heat treatment depicted in the T.T.T. curve shown in FIG. 1.

The Ti-30 at Nb-30 at Zr 7 at Ta alloy is first heated to a temperaturein the B region at a tempera ture higher than the peritectoidtemperature (about 775C), whereby a B solid solution structure havinguniform grains is formed. In this case, the treatment temperature T,,and the treatment time t, are determined by the chemical composition ofthe alloy. However, within the B phase region, a recrystallized regionis preferably chosen where the crystal grains are comparatively finelymaintained. A preferable treatment is to heat the alloy at a temperatureT, of 850*950C and at a time t, of 1-5 hours. After the alloy is heattreated in the B region, the sample is cooled, preferably quenched tomaintain the B solid solution structure. Thereafter, the cooled alloy iscold worked (N,) which enables the peritectoid reaction, in thesubsequent peritectoid (B- B'+B") heat treatment to be easily andthoroughly conducted. If the cold working step is not performed, theperitectoid in the grain boundary or the inner portions of the grainparticles is not uniform. In order to prevent this nonumiformity and topromote the peritectoid reaction, the cold working step N, is performedat a working rate of more than 50%, perferably more than 90%.

After the alloy has been cold worked in the N, step, the alloy is heatedwithin the B'+B" region, whereby a peritectoid B+B" structure isachieved by decomposition of the solid solution B structure. In thisphase of theheat treatment in order to attain the peritectoid structure,there is not as great dependency between the T treatment temperature andthe treatment time 2 within the peritectoid region as in the case of theB heat treatment. However, the treatment time t, largely depends on thepreceding cold working N, step. Thus, the larger the N, step, theshorter the treatment time. If the treatment time t, takes longer, thesuperconducting characteristics of the alloy deteriorate. It is believedthat the distance between the two phases is increased and the strainenergybetween the layer walls is reduced. The main point is that thetreatment temperature and the time should be selected to maintain theperitectoid reaction in its latent period or initial stage,

which can be determined by electrical resistance measurements, or bydetecting changes in the X-ray pattern. The preferred peritectoid heattreatment is a temperature T of 400-700C at a time t, of [-5 hours. Theperitectoid heat treatment is usually done once, but a more fineperitectoid structure can be made by repeating this treatment at leasttwice. In the peritectoid heat treatment, in order to improve the coldworkability of the alloy for the subsequent cold working step,precipitation of the at phase by a eutectoid reaction (B- oz+/3") shouldbe avoided. Further, in the precipitation heat treatment of the a phasein the final heat treatment step, in order to finely precipitate the aphase or the to phase, the a (+w) phase should not be present in thealloy which is to be treated in the a phase precipitation heat treatmentstep. If the a phase is present, the a phase grows during the a phaseprecipitation heat treatment and fine precipitation of the a phasecannot be attained, which means that the a (+B) phase is neverprecipitated in the peritectoid heat treatment. All of this means thatthe earlier described limited heat treatment is necessary. Further, thecooling step after the peritectoid heat treatment is preferably aquenching step which maintains the peritectoid structure. The hardnessof the alloy sample after the peritectoid heat treatment is slightlyless when compared to the hardness of the sample after the cold workingN, step and the workability is substantially improved.

The cold working step N is performed to refine more thoroughly the twophase grain structure after the peritectoid heat treatment, and toprovide a sufficient dislocation network to increase the number of a-phase precipitating nuclei from which grains grow when the next a phaseprecipitation heat treatment is conducted in order that theprecipitation of the a (+m) phase is easily and completely performed.The cold working step is conducted at a working rate of more than 50%,preferably more than The final heat treatment step converts the alloysample which has achieved the fine two phase separation structure toanother structure by the a phase precipitation heat treatment. In thefinal heat treatment the fine B'+B" peritectoid structure is convertedto a fine B'+B"+a (+1) multi-phase eutectoid structure. In the a phaseprecipitation heat treatment, the treatment temperature T, is notcritical within the a phase precipitation region in relation to thetreatment time However, the treatment time I, depends on the coldworking of the preceding N and N, steps, and the preceding peritectoidheat treatment (T If the structure is sufficiently refined by thepreceding cold working and heat treatment steps, the treatment time t,is decreased. If the treatment time 1 is unnecessarily long, thesuperconducting characteristics of the alloy deteriorate. In themulti-phase separation heat treatment, the treatment temperature and thetreatment time are also chosen such that the multi-phase separationreaction stops at the latent period or initial stage of the a phaseprecipitation. The preferred a phase treatment conditions aretemperatures T ranging from 450-600C and times 2 of 1-5 hours. Further,this multi-phase separation heat treatment is usually performed once,but a more fine multi-phase separation structure can be achieved byrepeating this treatment at least twice.

In order to provide the alloy with a finer nonhomogeneous structureafter the final a phase precipitation heat treatment, a cold workingstep N is performed. This cold working step N provides a finer alloystructure and also strengthens the dislocation networks at thenon-homogeneous point to improve the superconducting characteristics (lccharacteristics). The cold working step N is performed at a working rategreater than 50%, preferably greater than 90%.

By the process of the present invention, the Ti-Nb- Zr-Tasuperconducting alloy, when subjected to the described working and heattreating procedures, is altered to a very fine multi-phase ,8+B"+a(+m)separationstructure which is non-homogeneous. By this procedure thesuperconductive characteristics (lc characteristics) of the alloymaterial are improved.

The method of treatment of the present invention is applicable tosuperconducting alloys such as the quaternary Ti-Nb-Zr-Ta alloys.However, the chemical compositions of the alloy materials which aretreated by the method of the present invention are limited by thedifferent superconducting characteristics required of thesuperconducting alloys. These characteristics include transitiontemperature Tc, critical current value Ic, critical magnetic field Her,and the like. For instance, the presence of Nb in quantities less thanat decreases the temperature Tc while the value Ic at the boiling point4.2l( of liquid helium substantially deteriorates. If Nb is present inquantities less than 50 at the Pier value decreases which means that theNb content of the alloy should be limited within 20-50 at If Zr ispresent in quantities less than 10 at the value of I shows noimprovement, while if the Zr content is greater than at the Her and lovalues and the cold workability of the alloy'dete ri5rate. TEEETHE Zrcontent is limited to values ranging from 10-40 at Ti shows no effectfor the improvement of the Tc,

lo and Her values in quantities less than 10 at while in quantitiesgreater than SO at the I valuesdetgrig; rate. Thus, the content of Tishould be within the range of 10-50 at Ta has an effect on theimprovement of the Her and Ic valuesias'well asthe wenaismwme alloy. Thepresence of Ta makes it possible to carry out the method of theinvention. When Ta is present in amounts less than 5 at no improvementin the Te, lc and Hcr values in quantities less than 10 at while inquantities greater than at the lc values deterio- The object of thepresent invention was to provide an alloy which has a relatively highcritical magnetic field and a high critical current value at an externalmagnetic field less than KOe. One of the features of the presentinvention is the Ti-Nb-Zr-Ta superconducting alloy which consists of10-50 at Ti, 20-50 at Nb, 10-40 at Zr, and 5-12 at Ta and the usualimpurities. Havmg generally described this invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided herein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

EXAMPLE I.

The Ti-Nb-Zr-Ta alloys of the invention which have differentcompositions are melted and then manufactured into products. Anysuitable method can be used for melting and manufacturing the alloy.However, according to the present invention, a sponge, powder, particleor the like mixture consisting of the desired Ti,Nb, Zr and Taconstituents is melted in a water cooled copper mold under an inertatmosphere by means of a tungsten arc lamp to form an ingot having adiameter of 15mm and a length of 40mm. The ingot is vacuum-sealed in asteel pipe and then hot forged. The forged ingot piece is drawn into awire having a diameter of 0.25mm after annealing to provide a series oftest pieces.

FIG. 5 (a and b) shows the value of the critical magnetic field measuredfor 0.25mm diameter test pieces of Ti-Nb-Zr-Ta quaternary alloys havingdifferent compositions which are subjected to a solution heat treatmentfor 5 hours at 1000C in vacuum. In the measurement of the criticalmagnetic field. of the alloy, a pulse magnetic field was applied at thetemperature of liquid helium (4.2l() and the magnetic field was measuredunder conditions in which the test: pieces show normal conductingproperties.

FIG. 6 shows the critical magnetic fields of the Nb- Ti-Zr-Ta quaternaryalloys containing 30 at Nb, 30 at Zr and variously changing Ti and Tacontents.

It can be seen from FIGS. 5 and 6 that the Ti-Nb-Zr- Ta quaternaryalloys within the range of the composition of the present invention showhigh critical magnetic fields. Particularly, it can be seen from FIG. 6that when the Ta content is in the range between 5 and 12 at thecritical magnetic field is substantially improved.

The alloy of the invention has improved superconducting characteristicsas well as improved mechanical properties over the conventional alloys.That is, the Nb-Zr alloys and the Ti rich-Nb-Zr alloys have been knownas alloys of low workability, but the alloys of the present inventionhave a cold workability of 99%, and are satisfactorily applicable undersevere working conditions.

FIG. 7 shows the critical current value measured for a wire having adiameter of 0.25mm which is made of a superconducting alloy containing33 at Ti, 30 at Nb, 30 at Zr and 7 at Ta which has been heat treated at550C for one hour after cold working in each step and drawn into a wire.For purposes of comparison, a critical current value of a Nb-25Zrsuperconducting alloy in the form of a wire having a diameter of 0.25mm,which is commercially available on the market, is also shown. It can beseen that the alloy of the invention has a high critical current valuein external magnetic fields less than 70 KOe.

The material of the present invention can be advantageously used forsuper-conductive magnet wires for MHD generators which is a newdevelopment in the energy industry; in coils of superconductingtransformers or the like; .and in the exciting coils of DC generatorswhich makes it possible to compact the devices by increasing theexciting force by use of wires having a large critical current.

EXAMPLE 2 A 100g amount of a mixture ofTi, 30 at Nb, 30 at Zr and 7 atTais melted by means of an arc to form an ingot havin g a diahieter oflTnifiTThh1jgot is v??- um-sealed in a steel pipe after being coatedwith a foil of Ta and then is hot forged. A number of rod shaped testpieces having a diameter of 7mm are formed by cutting the outer shelland the rod. The test pieces are heated to the B phase region at atemperature of 850C (T for 2 hours and then water quenched to form testpieces having the [3 solid solution structure with a uniform grain.Then, the test pieces are cold swaged (N into a wire having a diameterof 2.5mm (the working ratio is about 87%). The wire test pieces are thenheat treated at three temperatures of 850C, 650C and 550C (T for 1-50hours and then water quenched. The temperature of 850C is the B phaseregion, the temperature of 650C is the peritectoid region and thetemperature of 550C is the a (-l-m) phase region. Then, each of the testpieces is enclosed in an OFHC copper tube, and is cold drawn (N) toreduce the cross sectional area by 90% to form a wire having a diameterof 0.8mm. The drawn test pieces are heat treated at 550C (T for -1000minutes and then finally cold drawn (N to reduce the cross sectionalarea by 90% to form a superconducting wire with a diameter of 025mm.

FIG. 2 shows the effect of the peritectoid treatment on the criticalcurrent value Ic of the prepared superconducting wire having a diameterof 0.25mm in an external magnetic field of 60 KOe at a temperature of4.2K. The histories of five test pieces Nos. l-5 are shown in FIG. 2 anddescribed in Table I.

TABLE I History of Test Pieces As can be seen from FIG. 2, if the secondstage intermediate heat treatment is conducted under the same conditionsas the a phase precipitating heat treatment, the materials which havebeen treated by a first stage 5 intermediate heat treatment at atemperature in the peritectoid region, i.e. at 650C for 3 hours and for50 hours, show higher critical current values than the materials treatedin the B phase region, i.e. at 850C for 3 hours. Further, even if thefirst stage intermediate 10 heat treatment of the alloy is conducted ata temperature in the peritectoid region, the heat treatment in theinitial stage, i.e. at 650C for 3 hours, shows higher critical currentvalues than the alloys which have been heat treated under completeperitectoid conditions, i.e. at

l5 650C for 50 hours. Even if the first stage intermediate heattreatment is performed in the a phase precipitation region, i.e. at 550Cfor 3 hours, a high critical current value is obtained for the alloysimilar to the alloy heat treated at 650C for 3 hours. However, theworkability of the alloy is less so that further working is difficult.Therefore, it is desirable from the viewpoint of the critical currentvalue and the workability that the first stage intermediate heattreatment be conducted in the peritectoid region, preferably for a shorttime.

FIG. 3 shows the relation between the critical current value and theX-ray integrated intensity I (a+m) of the a phase and the to phase forthe second stage intermediate heat treatment (the a phase precipitationheat treatment) time (1 of test piece No. 3 of Table 1. After the twophase separation heat treatment at 650C for 3 hours, the a phase and the1 phase are not significantly present, but as the a phase precipitationheat treatment is prolonged, first the (0 phase appears and then theX-ray integrated intensity of the 0: phase increases. The X-rayintegrated intensity I (a+w) increases as the time passes, but the lineprofiles of the X-ray of the 0) phase and the a phase extend largely inthe initial stage of the precipitation. This means that the precipitatesof the wphase and the aphase are very fine. After the critical currentvalues at a maximum of 550C are obtained for 100 minutes, the lineprofile of the X-ray becomes sharp. Thus, it may be that theprecipitated grains grow into an over aging condition. Therefore, it isdesirable from the viewpoint of the inverse effect caused by the overaging action on the critical current value, that the precipitation ofthe grains in the a phase and the to phase be satisfactorily conapnea...

TABLE II History of Test Pieces It is apparent from FIG. 4 that when theTi-30 at bib-30 at Zr-7 at Ta alloy is treated in the peritectoid regionat 650C for [-3 hours, is cold drawn in a reduction separation range at550C for 100 minutes and then is cold drawn for a 90% reduction, a highcritical current density (,lc) is uniformly obtained in large externalmagnetic fields (H). Furthermore, the 10 value is greater than that ofthe The tensile strength of the alloy as a mechanical property of testpieces Nos. 1 and 3 shown in Table l was measured. The measurementsobtained show that the tensile strength of test piece No. l was 140kg/mm and test piece No. 3 was 160 Kglmm It can be seen that the tensilestrength of the superconducting alloy wire treated by the method of thepresent invention is very high. (The heat treatment time during the aphase precipitation heat treatment was 100 minutes.) The criticalcurrent density in the external magnetic field of 70 KOe was more than 5X A/cm As is apparent from the above description, the method oftreatment of superconducting alloys of the present invention comprisesthe steps of heat treating the alloy in the peritectoid range,subjecting the alloy to an a phase precipitation heat treatment and coldworking the alloy between the heat treatments whereby an alloy of a fineand non-homogeneous structure is obtained. The method of treatment makesit possible to improve the critical current value of the alloy over awide range from a low magnetic field of 30 KOe to a high magnetic fieldof 90 KOe. It has also been found that the addition of Ta to the alloycomposition improves the workability. ln addition the peritectoid heattreatment and the a phase precipitation heat treatment are conductedindependently of one another which improves the peritectoid structureand workability of the alloy. Furthermore, among the many advantages ofthe present invention is that the peritectoid heat treatment and the aphase precipitation heat treatment can be performed at a temperatureless than 700C which alleviates the problem caused by the reaction ofthe alloy with the copper coating.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed is:

1. A method of working and treating Ti-Nb-Zr-Ta superconducting alloyconsisting of 10-50 at Ti, 20-50 at Nb, 10-40 at Zr and 5-12 at Ta toachieve a fine and non-homogeneous structure which comprises the stepsof:

by heating the alloy to a temperature within the B solid solution range;

cooling and cold working said heated Ti-Nb-Zr-Ta alloy;

heating said cold worked alloy to a temperature within the (B'+B") phaseregion and then cooling said heated (B'+ alloy to maintain theperitectoid structure;

cold working the peritectoid alloy;

forming a multi-phase ,B'+B"+a (cu) eutectoid alloy structure by heatingsaid peritectoid alloy to a temperature within the (,8i-,B- B+B+a(+w)eutectoid structure range and then cooling said eutectoid alloy; and

cold working the eutectoid alloy.

1. A METHOD OF WORKING AND TREATING TI-NB-ZR-TA SUPERCONDUCTING ALLOYCONSISTING OF 10-50AT%TI, 20-50AT%NB, 10-4OAT%ZR AND 5-12AT%TA TOACHIEVE A FINE AND NONHOMOGENEOUS STRUCTURE WHICH COMPRISES THE STEPSOF: FORMING A B SOLID SOLUTION OF SAID TI-NB-ZR-TA ALLOY BY HEATING THEALLOY TO A TEMPERATURE WITHIN THE B SOLID SOLUTION RANGE; COOLING ANDCOLD WORKING SAID HEATED TI-NB-ZR-TA ALLOY; HEATING SAID COLD WORKEDALLOY TO A TEMPERATURE WITHIN THE (B''+B") PHASE REGION AND THEN COOLINGSAID HEATED (B''+B") ALLOY TO MAINTAIN THE PERITECTOID STRUCTURE; COLDWORKING THE PERITECTOID ALLOY, FORMING A MULTI-PHASE B''+B"+A (W)EUTECTOID ALLOY STRUCTURE BY HEATING SAID PERITECTOID ALLOY TO ATEMPERATURE